V6 Tdi Starting Problems

Helloo. I'm having a odd fault with my 2005 3.0 v6 Touareg. Its starts perfectly when cold but when upto temp it sounds like a flat battery when trying to start. Always starts second or third time but it's getting a little annoying now. I've scanned several times and while I don't have a log to post up at the moment (I will update with one) the appears to be no stand out codes that suggest starting faults. There is a fault about low voltage which I'll add the code as follows -

00668 - supply voltage terminal 30. 02 lower limit exceeded - intermittent. I'd suspect the battery to be fine tho as starting cold is no issues.

My question was mainly to establish how others on here would approach such an issue and the best way to diagnose starting it voltage faults with the use of vcds? I have read posts about Q7s and other touaregs with the same problem and it pointed to a temp sensor, presume I could check these through live data/measuring blocks?

Apologies I'm a bit of a novice.

Thanks
Kevin

Kevin_w90 said:

Its starts perfectly when cold but when up to temp it sounds like a flat battery when trying to start.

Click to expand...

Can you elaborate more what you mean?

To me a "sounds like a flat battery" implies that it cranks over more slowly.

I'd probably start by logging the RPM while cranking it, both cold and hot.

-Uwe-

Hi Uwe,

Thanks for the reply. The first attempt when it's hot it just cranks very slowly once then stops. Next turn of the key it turns over quickly (as per normal) and fires up. There's a video on YouTube where someone has the same symptoms, attached the link below (unsure if attaching links is allowed).

https://m.youtube.com/watch?v=v-32E24AXdk

The comments suggest a faulty temp sensor caused this one but I've seen multiple fixes being posted on other sites.

Thanks

OK, monitor "battery voltage" in the ECU while cranking and it's in the mode where it will barely turn over. How low does the voltage the ECU shows go? Do the the same directly at the battery (or at the "jump start" terminals under the hood) with a volt meter. How low does that voltage go?

-Uwe-

Awesome, thanks! I'll try this tommrow and report back. Thanks again

Isn't that called latent heat hot start or a result of timing being out or forced advanced too & bind a hot motor crank from a sensor being out such as ECT or even IAT, in addition a bad ground can cause this in excessive hot climates to the starter or the starter could be cooked from a heat shield being missing or grease just plain run out in starter bearings from age?

Shouldn't you log all "G" sensors for cold to hot linear transition and then park truck after hot and shut down motor, then observe a log during cool down to simulate the condition linear back down of all G sensors looking for anomaly?

Then before cranking log the voltage like Uwe aforementioned during condition, right?

Did you make sure a stored vacuum isn't leaking into an anti start shut down flap or sticking to block air intake or TV function for angle if supported?

An auto-scan and review of the SSP can be most helpful in situations like this huh?